Road loads are forces and moments acting at suspension, body and powertrain interface locations in vehicles. Accurate road loads are essential for the design and verification of vehicle durability performance. Road loads are typically measured by driving the vehicle over the proving ground surfaces specifically designed for testing vehicle durability, and taking measurements of the response of vehicle system components. These tests are costly and time-consuming as they require the development and fabrication of design-intent vehicle prototype and extensive instrumentation. Additionally, the processing of substantial amounts of measured data is quite time consuming. This time and labor intensive process is particularly disadvantageous during the prototyping stages of the vehicle design as the rapid feedback of performance information is vital to the design changes in the least amount of time.
Past attempts at predicting road loads using theoretical techniques have been less than completely successful. Analytical predictions of road loads are made difficult by the fact that tires undergo severe deformation while traveling over durability proving-ground surfaces. Existing tire models have been found to be inadequate, either because they are too simple (efficient but not accurate) or too complex (accurate but not efficient for computer simulations).
One known analytical technique for road load predictions uses the concept of a virtual tire testing strategy, based on an ETA/VPG generated tire model. VPG (“Virtual Proving Ground”) is an integrated software package offered by Engineering Technology Associates, Inc., for the simulation and analysis of nonlinear dynamic problems such as durability and road load prediction. It uses software known as LS-DYNA which is a general purpose transient dynamic finite element program capable of simulating complex, real world problems. Using the software described above, an effective road profile is generated in a simulation (explicit analysis) environment, which is then utilized to predict behavior of simplified quarter car model. Examples of other analytical techniques used to model tire behavior are disclosed in U.S. Pat. Nos. 5,750,890; 5,900,543; 6,112,586; and 6,134,957, all of which are assigned to the assignee of the present invention.
Other commercially available tire models exist for simulating rough road loads for vehicles. The most commonly used tire models of this type include: MSC/ADAMS 2D and 3D tire models; MSC/F-tire model; LMS/CD Tire model; TNO/SWIFT model; and ETA/VPG model. Except for ETA/VPG tire model, the other above-mentioned models are used for simulation in multibody environment (e.g., ADAMS, DADS Software). These commercially available multibody dynamics simulation programs are used to simulate the dynamics of the multiple, interconnected rigid and flexible bodies found on vehicles. The behavior of the multibody system on the vehicle is described by the appropriate equations of motion, with emphasis on the vehicle's suspension system.
The VPG tire model is developed for vehicle simulations in FE (finite element) environment (e.g., DYNA Software). All of these tire models have been found to be inadequate in simulating durability loads for various reasons such as accuracy and computational time.
Accordingly, there is a need for a complete system for predicting rough road loads for full vehicle system. The present invention is intended to satisfy this need.